1. Field of the Invention
This invention relates to a method for producing a hydraulic binder using a preheater type cement clinker producing installation. Specifically, the invention includes the removal of a portion of the heated gases from the installation, in which gases is entrained a selected quantity of calcium oxide. The entrained calcium oxide is a product of the preheating finely ground of raw material in a preheating zone of the installation. The gas and entrained material are processed, separated and the calcium oxide is then slacked, or hydrated.
2. Description of the Prior Art
Hydraulic binder possessing the requisite qualities for use as a masonry mortar or plaster are commonly produced using furnaces or small kilns in which the limestone is thermally processed at temperatures between 450.degree. C. and 900.degree. C. These temperatures are relatively low compared to the extremely high temperatures required to produce cement clinker. In a typical cement clinker production installation utilizing a preheater tower and a rotary kiln, material temperatures of up to 1500.degree. C. and gas temperatures of up to 2400.degree. C. are common in the kiln. Consequently the typical furnaces required to process raw material to produce the hydraulic binder are structurally smaller and less expensive than the equipment commonly used in cement production.
Nevertheless, the furnaces or small kilns necessary to achieve temperatures of 450.degree. C. to 900.degree. C. require substantial capital investment. It has been recognized that it is economically and practically feasible to utilize an existing cement clinker production installation or cement plant to produce a hydraulic binder, thus eliminating the necessity of constructing and operating a separate facility for producing the hydraulic binder For example, U.S. Pat. No. 4,236,932 and U.S. Pat. No. 4,298,340, both to Herchenbach et al., disclose a method and apparatus, respectively, for producing a hydraulic binder with a preheater type cement kiln system in common use. This kiln system includes a suspension type preheater or a series of preheating cyclones contained in a preheater tower in connection with a rotary kiln. Such a kiln system using preheaters is designed to partially process and decarbonize or calcine the finely ground raw material, thereby allowing a smaller rotary kiln to be used than would otherwise be required. This lowers energy consumption, reducing both energy costs and capital investment in producing cement. In such an installation, the raw material is partially calcined or decarbonized to various degrees in the sequential preheater stages. This partially calcined raw material is suitable for use in the production of a hydraulic binder. Since cement clinker production requires that certain process conditions, such as gas and material temperatures and material quantities, be maintained, the removal of partially calcined material can adversely affect the process.
The above patents to Herchenbach teach providing removal points below various preheater cyclones for removing a portion of the processed and partially precalcined meal. This method and apparatus is claimed to be economically feasible because only a portion of the processed meal is withdrawn as a hydraulic binder, while the remaining meal is sintered in the rotary kiln for the production of cement clinker. The disadvantages of using this system include the likelihood of adversely affecting the necessary thermal conditions in the entire system by the withdrawal of the processed meal from below the lower cyclones. Further, additional capital investment is required for the retrofit of valves, material outlet lines, and the associated apparatus used therewith.